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    <script>
      /*
        [[Prototype]] __proto__ 作用
        1. 是一个对象
        2. 这个对象可读可写
        3. 实现了继承
        */

      const a = {
        // __proto__: { uname: "jack" }
      };
      a.__proto__ = { uname: "jack" };
      console.log(a.__proto__.uname); //jack
      console.log(a.uname); //jack
    </script>
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